1. Field of the Invention
The present invention relates to a method and apparatus for dermatological tissue treatment, and more particularly, to controlling dosage from an electromagnetic source based on measurements of a handpiece motion and/or skin tissue response.
2. Description of the Related Art
Many electromagnetic dermatological treatment systems require extensive training before physicians and nurses develop the skills to deliver energy uniformly over a treatment region, such as the face, neck, chest, or back. In many cases, physicians and nurses do not treat uniformly, resulting in uneven treatment, over treatment, or under treatment. There is a need to create more uniform photothermal and/or radio-frequency (RF) treatment, particularly for large areas.
Additionally, not all patients respond the same way to the same level of treatment. So even if precisely the same laser energy dose is delivered to two different patients, the response of each patient may be substantially different. Within a single patient, the skin response may vary from region to region. Treatment of the forehead may respond differently than treatment of the neck, for example. If uniform treatment parameters are used for all patients or for all regions, then the treatment parameters will typically be designed for the most sensitive patient or the most sensitive region in order to avoid undesirable side effects. Designing for the most sensitive region or patient will frequently lead to undertreatment of other regions or patients.
Many medical laser systems for the treatment of dermatological skin conditions function by pressing a footpedal to trigger the delivery of a single pulse of treatment energy. This type of treatment apparatus is slow and has a lot of repetitive motions, which can be tiring to the operator. Other laser treatment systems fire identical pulses at a constant pulse repetition rate as the user moves the handpiece across the tissue. This system requires skill and increases the risks of over-or under-treatment in the hands of an unskilled operator. Therefore, there is also a need for an approach to electromagnetic treatment that provides controlled dosage and adjusts the dosage level in real time to prevent over-and/or under-treatment.
Weckwerth U.S. Pat. No. 6,758,845 describes the use of optical measurements of regularly spaced indicia that are placed on or adjacent to the treatment region, but the concept is limited by the application of regularly spaced indicia that are counted to measure distance traveled by a handpiece. This requires the precise positioning of indicia to avoid errors. In addition, the visible indicia may be difficult to remove following treatment, and may leave an unsightly pattern on the skin following treatment.
Weckwerth '845 and Talpalriu U.S. Pat. No. 6,171,302 describe mechanical roller systems for tracking handpiece travel. These can be unreliable, for example, when used with gel due to a lack of friction between the mechanical roller and the skin surface. This leads to drop outs and errors in measurements of positional parameters. In addition, mechanical rollers can become rusted or gummed up so that they no longer spin easily, which makes dropouts and errors more likely. Wearing out of mechanical parts leads to similar errors.
Weckwerth '845 describes other systems that measure position of the handpiece indirectly, through the interaction with reference planes or points outside the target area, rather than measuring the target area directly. With this approach, the location of the treatment surface relative to the reference surface must be measured or controlled. In addition, these systems only measure one coordinate for the handpiece, which means that motion of the handpiece across the target tissue due to change in orientation of the handpiece may not be accounted for by the sensor systems. This leads to inaccuracies.
For treatment of large areas, an automatic laser control system is needed for adjusting laser treatment parameters in real time in response to the handpiece position, velocity, and/or acceleration or in response to the laser treatment itself. Thus, there is a need for an apparatus and method for a feedback loop that increases the effectiveness of treatment by controllably responding to treatment variables such as treatment speed, handpiece angle, handpiece acceleration, patient to patient variability, region to region variability within the same patient, etc. There is also a need for an apparatus and method that preferably enable faster and more reproducible treatments, that require less training and skill by the operator and/or that controllably respond to treatment variables. The apparatus and method preferably will also increase effectiveness without increasing side effects or invasiveness, treat with lower pain and side effects, directly measure treatment efficacy and/or progress for use in a feedback loop either alone or with other inputs instead of relying primarily on accurate delivery of a predetermined treatment dosage or on measurement of handpiece positional parameters, monitor biological response and treatment variables for improved biological predictability, efficacy, and safety, and/or permit better control of dosage, for example for photo-dynamic therapy (PDT) treatments, laser hair removal, or fractional laser resurfacing.